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Issue 11, 2014
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Comparing new and conventional methods to estimate benthic algal biomass and composition in freshwaters

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Abstract

We compared conventional microscope-based methods for quantifying biomass and community composition of stream benthic algae with output obtained for these parameters from a new instrument (the BenthoTorch), which measures fluorescence of algal pigments in situ. Benthic algae were studied in 24 subarctic oligotrophic (1.7–26.9, median 7.2 μg total phosphorus L−1) streams in Northern Sweden. Readings for biomass of the total algal mat, quantified as chlorophyll a, did not differ significantly between the BenthoTorch (median 0.52 μg chlorophyll a cm−2) and the conventional method (median 0.53 μg chlorophyll a cm−2). However, quantification of community composition of the benthic algal mat obtained using the BenthoTorch did not match those obtained from conventional methods. The BenthoTorch indicated a dominance of diatoms, whereas microscope observations showed a fairly even distribution between diatoms, blue-green algae (mostly nitrogen-fixing) and green algae (mostly large filamentous), and also detected substantial biovolumes of red algae in some streams. These results most likely reflect differences in the exact parameters quantified by the two methods, as the BenthoTorch does not account for variability in cell size and the presence of non-chlorophyll bearing biomass in estimating the proportion of different algal groups, and does not distinguish red algal chlorophyll from that of other algal groups. Our findings suggest that the BenthoTorch has utility in quantifying biomass expressed as μg chlorophyll a cm−2, but its output for the relative contribution of different algal groups to benthic algal biomass should be used with caution.

Graphical abstract: Comparing new and conventional methods to estimate benthic algal biomass and composition in freshwaters

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Publication details

The article was received on 11 Jun 2014, accepted on 18 Sep 2014 and first published on 19 Sep 2014


Article type: Paper
DOI: 10.1039/C4EM00326H
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Environ. Sci.: Processes Impacts, 2014,16, 2627-2634

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    Comparing new and conventional methods to estimate benthic algal biomass and composition in freshwaters

    M. Kahlert and B. G. McKie, Environ. Sci.: Processes Impacts, 2014, 16, 2627
    DOI: 10.1039/C4EM00326H

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